Plate heat exchanger assembly with enhanced heat transfer characteristics

ABSTRACT

A plate heat exchanger for accommodating a circulating refrigerant and heat transfer fluid. The plate heat exchanger includes a plurality of heat transfer plates and at least one electrode plate. The plurality of heat transfer plates are mounted in parallel relationship to each other defining alternating flow spaces for a refrigerant and a heat transfer fluid. The electrode plate is located in each refrigerant flow space and is spaced from the adjacent heat transfer plates. The electrode plate includes outer electrode surfaces on each side thereof to produce an electric field. The effect of the electric field is an increase in the heat transfer rate between the refrigerant and heat transfer fluid. The invention also includes a method of exchanging heat between a heat transfer fluid and a refrigerant in a plate heat exchanger.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to heat exchanger evaporators andcondensers, particularly those used in HVAC applications. The inventionrelates to a plate heat exchanger evaporator, where the refrigerantflows through the plates and evaporates, while a heat transfer fluidflows through adjacent plates and is cooled by the evaporatingrefrigerant. The invention also relates to a plate heat exchangercondenser. In a preferred embodiment, the evaporator is a component of arefrigeration system which can be used for cooling large quantities ofwater. This invention relates to an apparatus and method for increasingthe heat transfer rate of these types of heat exchangers.

[0003] 2. Description of the Related Art

[0004] Refrigeration systems of the type used to cool large quantitiesof water typically include a heat exchanger evaporator having separatedpassageways. One passageway carries refrigerant, and another carries theheat transfer fluid to be cooled, usually water. As the refrigeranttravels through the evaporator, it absorbs heat from the heat transferfluid and changes from a liquid to a vapor phase. After exiting theevaporator, the refrigerant proceeds to a compressor, then a condenser,then an expansion valve, and back to the evaporator, repeating therefrigeration cycle. The fluid to be cooled passes through theevaporator in separate fluid channels and is cooled by the evaporationof the refrigerant. The fluid can then be routed to a cooling system forcooling the spaces to be conditioned, or it can be used for otherrefrigeration purposes.

[0005] It is desirable to optimize the heat transfer rate between fluidsflowing through a heat exchanger, particularly large heat exchangersused in heating and air conditioning systems. A number of approacheshave been proposed to improve the heat transfer characteristics ofevaporators and condensers. One generally known approach is to create anelectric field on a heat transfer surface in order to improve heattransfer. The use of an electric field to improve the heat transfer ofconvection heat transfer in a liquid is generally referred to as theelectrohydrodynamic effect or EHD. Applications of this approach aredisclosed in U.S. Pat. No. 4,651,806 to Allen et al., U.S. Pat. No.5,072,780 to Yabe, and U.S. Pat. No. 5,769,155 to Ohadi et al.

SUMMARY OF THE INVENTION

[0006] The object of the present invention therefore is to provideimproved heat exchanger methods and systems. Another object is toprovide improved heat exchangers for HVAC applications that are moreefficient and more compact than conventional heat exchangers.

[0007] The advantages and purposes of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theadvantages and purposes of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe appended claims.

[0008] To attain the advantages and in accordance with the purposes ofthe invention, as embodied and broadly described herein, the inventionincludes a plate heat exchanger for accommodating a circulatingrefrigerant and heat transfer fluid. The plate heat exchanger includes aplurality of heat transfer plates and at least one electrode plate. Theplurality of heat transfer plates are mounted in parallel relationshipto each other defining alternating flow spaces for a refrigerant and aheat transfer fluid. The electrode plate is located in each refrigerantflow space and is spaced from the adjacent heat transfer plates. Theelectrode plate includes outer electrode surfaces on each side thereofto produce an electric field. The effect of the electric field is anincrease in the heat transfer rate between the refrigerant and heattransfer fluid. The plate heat exchanger typically includes a pluralityof refrigerant flow spaces and corresponding electrode plates locatedtherein.

[0009] In a further aspect of the invention, the invention includes aplate heat exchanger for accommodating two circulating heat exchangemediums. The plate heat exchanger includes a plurality of heat transferplates and an electrode plate. The plurality of heat transfer plates aremounted in parallel relationship to each other to define alternatingfluid channels comprising first and second fluid channels. The firstfluid channel is for containing a first heat exchange medium, and thesecond fluid channel is for containing a second heat exchange medium. Anelectrode plate is located in each first fluid channel and is positionedgenerally parallel to and spaced from the heat transfer plates. Theelectrode plate includes outer electrode surfaces on each side thereofto produce an electric field. Either the outer electrode surfaces ofeach electrode plate, or the surfaces of the heat transfer platessurrounding each electrode plate and defining the first fluid channel,include surface irregularities. The effect of the electric field on thesurface irregularities is an increase in the heat transfer rate betweenthe first heat exchange medium and the second heat exchange medium.

[0010] In a yet further aspect of the invention, the invention includesa method of exchanging heat between a heat transfer fluid and arefrigerant in a plate heat exchanger. In the method of the presentinvention, a plurality of parallel heat transfer plates are provided. Anelectrode plate is also provided inside each of a plurality of firstflow spaces defined by first surfaces of adjacent heat transfer plates.Next, a refrigerant is flowed through the plurality of first flowspaces, and a heat transfer fluid is flowed along a second surface ofeach of the heat transfer plates. The second surfaces of adjacent heattransfer plates to define a second flow space for the heat transferfluid. Lastly, a voltage is applied to the electrode plates to create anelectric field, the electric field increasing the heat transfer ratebetween the refrigerant and the heat transfer fluid. The method may alsoinclude the step of forming surface irregularities on either the firstsurfaces of the heat transfer plates or on the surfaces of the electrodeplates.

[0011] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which are incorporated in andconstitute a part of this specification, illustrate several embodimentsof the invention and together with the description, serve to explain theprinciples of the invention.

[0013] In the drawings,

[0014]FIG. 1 is a cross-sectional side view of a plate heat exchangeraccording to the present invention;

[0015]FIG. 2 is a front view of a first heat transfer plate of the plateheat exchanger of FIG. 1, prior to assembly;

[0016]FIG. 3 is a front view of a second heat transfer plate of theplate heat exchanger of FIG. 1, prior to assembly;

[0017]FIG. 4 is a front view of the first heat transfer plate of theplate heat exchanger of FIG. 1, after the first heat transfer plate hasbeen stacked onto the second heat transfer on plate;

[0018]FIG. 5 is a front view of a heat transfer plate with an electrodeplate placed on top of a heat transfer plate of FIG. 1;

[0019]FIG. 6 is a front view of an electrode plate of the plate heatexchanger of FIG. 1;

[0020]FIG. 7 is a partial cross-sectional view of an insulator for anelectrode plate according to an embodiment of the present invention;

[0021]FIG. 8 is a schematic cross-sectional view of the plate heatexchanger of FIG. 1 with the insulators and electrode plates removed;

[0022]FIG. 9 is a schematic cross-sectional view of the plate heatexchanger of FIG. 1 with the insulators and electrode plates installed;and

[0023]FIG. 10 is a cross-sectional side view of a plate heat exchangerwith an electrical connection structure in an alternative locationcompared to FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

[0025] While the present invention has broader application regarding aheat exchanger assembly for transferring heat between fluids flowing inthe spaces between a plurality of adjacent plates, the invention wasdeveloped and has particular application as an evaporator or condenserassembly in an HVAC chiller system. The plate heat exchanger will firstbe described as an evaporator for sake of ease of discussion. The use ofthe plate heat exchanger as a condenser will be briefly described laterin the specification.

[0026] In accordance with the present invention, a plate heat exchangeris provided with an increased heat transfer rate due to an electricfield created by an applied voltage on an electrode plate. The plateheat exchanger is generally comprised of a stacked array of heattransfer plates mounted in parallel relationship to each other, and aplurality of electrode plates.

[0027] In accordance with the present invention, the plate heatexchanger includes a plurality of heat transfer plates. In theembodiment shown in FIGS. 1-10, the plate heat exchanger 10 includes astacked array of first heat transfer plates 12 and second heat transferplates 14. The first heat transfer plates 12 and second heat transferplates 14 are stacked one on top of the other in a parallel relationshipto define alternating first and second flow channels 16 and 18,respectively. The specific shape of the heat transfer plates shown inthe drawings is only one example and should be used for explanatorypurposes only. The present invention is compatible with a wide varietyof heat transfer plate designs. As best shown in FIGS. 2-3 and 9, thefirst and second heat transfer plates 12 and 14 of the exemplary heatexchanger are in the shape of thin plates across which heat istransferred between two mediums. The thickness of the plates may bevaried depending upon the specific application. The plates 12 and 14 aretypically rectangular in shape, however, other shapes can becontemplated. The plates 12 and 14 are spaced apart parallel to eachother to define fluid channels that will be discussed below. The heattransfer plates 12 may be made out of any of a variety of materialsknown in the field, such as steel. The number and size of the heattransfer plates, and other components, depends on the requirements ofthe specific application.

[0028] In the embodiment shown in FIGS. 1-9, the heat transfer platesinclude a plurality of dimples. As shown in FIG. 2, the first heattransfer plate 12 has a plurality of alternating dimples in a grid-likepattern. For example, in FIG. 2, the dimples designated by referencenumber 20 (unshaded) are recesses going into the page, and the adjacentdimples designated by reference number 22 (shaded) are projectionscoming out of the page in FIG. 2. The dimples alternate between therecessed dimples 20 and projecting dimples 22 along each row and columnof dimples.

[0029] The dimple configuration is best illustrated in FIG. 9. In thefirst heat transfer plate 12 to the far left in FIG. 9, a projectingdimple 20 is formed in flat surface 24. The dimple 20 projects to theleft in FIG. 9, and is therefore called a projecting dimple. Theadjacent dimple on the first heat transfer plate (going upward in FIG.9) is a recessed dimple 22 formed in the flat surface 24 of the firstheat transfer plate 12. The dimple 22 is recessed to the right in FIG.9, and is therefore called a recessed dimple. The next dimple (goingupward in FIG. 9) after recessed dimple 22 is a projecting dimple 20.For sake of ease of discussion, the dimples will hereinafter be referredto by their particular function. The projecting dimples 20 of the firstheat transfer plate 12 will be referred to as insulator-engaging dimples20 because insulators (to be described) are positioned in them as willbe described in greater detail later in the specification. The recesseddimples 22 of the first heat transfer plate 12 will be referred to asstructural support dimples 22 because they provide structural support tothe heat exchanger by engaging with adjacent structural support dimples28 of the adjacent plate. The schematic of FIG. 9 shows a space betweenthe structural support dimples 22 and 28, however the structural supportdimples actually contact each other.

[0030] The dimples 20 and 22 can be of a variety of sizes and shapes. Inthe illustrated embodiment, the dimples are cylindrical and are formedby stamping the flat surface 24 of the first heat transfer plate 12. Anysuitable number of dimples may be provided, from 3 or 4 to severalhundred. The figures show an embodiment with 93 dimples, however, thisnumber can be greatly varied.

[0031] The second heat transfer plate 14 also includes a plurality ofdimples. As shown in FIGS. 3 and 9, the second heat transfer plate has aplurality of alternating recessed and projecting dimples which arealigned with the dimples of the first heat transfer plate. For example,immediately across from each insulator-engaging dimple 20 of the firstheat transfer plate is a similar insulator-engaging dimple 26 in thesecond heat transfer plate 14. The insulator-engaging dimple 26 of thesecond heat transfer plate projects in the opposite direction of thecorresponding dimple 20 of the first heat transfer plate. Immediatelyacross from each structural support dimple 22 of the first heat transferplate 12 is a similar structural support dimple 28 on the second heattransfer plate 14. The structural support dimple 28 of the second heattransfer plate 14 projects toward and contacts the correspondingstructural support dimple 22 of the first heat transfer plate 12. Thedimples of the second heat transfer plate 14 are stamped on the flatsurface 30 of the second heat transfer plate in a similar fashion asdescribed for the first heat transfer plate 12.

[0032] In plate heat exchangers, the heat transfer plates define a firstfluid channel 16 and second fluid channel 18 for a first heat exchangemedium and second heat exchange medium respectively. In a typical heatexchanger, the first heat exchange medium of the first fluid channels 16is a refrigerant, and the second heat exchange medium of the secondfluid channels 18 is a heat transfer fluid. Other types of fluids mayalso be used.

[0033] The first and second heat transfer plates define alternatingfirst fluid channels 16 and second fluid channels 18. As shown in FIG.9, a first fluid channel 16 is formed in the space between two adjacentheat transfer plates 12 and 14 in which an electrode plate, to bedescribed below, is located. The first fluid channel 16 is defined bythe flat surfaces 24 and 30 of the first and second heat transfer plates12 and 14. The refrigerant will flow inside of the first fluid channel16 and flow around the insulators, electrode plate, and structuralsupport dimples in the flow path of the first fluid channel. As will bediscussed, the electrode plates are placed substantially in the middleof the first fluid channels 16. The volume of refrigerant in the firstfluid channel 16 is a function of the space “s” between the flatsurfaces 24 and 30 of the first and second plates (FIG. 9), the width“w”, and the height “h” (FIG. 3) of the heat transfer plates. Theelectrode plate, insulators, and structural support dimples 28 also takeup some of the volume of the first fluid channels.

[0034] The fluid channels adjacent the first fluid channels are referredto as the second fluid channels or heat transfer fluid channels 18.Unlike the first fluid channels 16, the second fluid channels 18 do notcontain electrode plates or insulators, as illustrated in FIG. 9. Firstfluid channels 16 and second fluid channels 18 do not fluidlycommunicate with one another. The heat transfer fluid flows through thesecond fluid channels 18.

[0035] During operation of the plate heat exchanger, a first fluidcomprising a refrigerant flows in an upward direction inside the firstfluid channels 16, while a second fluid comprising a heat transfer fluidsimultaneously flows in a downward direction in the second fluidchannels 18. In the first fluid channels 16, the refrigerant absorbsheat from the water or other heat transfer fluid in the second fluidchannels 18 and evaporates in whole or part. In the second fluidchannels 18, the heat transfer fluid transfers heat to the refrigerant,and decreases in temperature.

[0036] In HVAC applications, the first fluid in an evaporator is arefrigerant. A variety of different types of refrigerants can be usedwith the present invention. Examples of refrigerants suitable for thepresent invention include, but are not limited to, R-22, R20 134a, andR-407C. The selection of the type of refrigerant can have an effect onother factors such as pressure drop in the fluid channels and the amountof heat transfer to or from the heat transfer fluid.

[0037] In accordance with the present invention, the heat exchangerincludes a plurality of electrode plates. As embodied herein and shownin FIGS. 5 and 9, an electrode plate 40 is located in each first fluidchannel 16, and includes outer electrode surfaces 42 on each sidethereof. The electrode plates also include holes 44 for the insulators,and holes 46 for the structural support dimples 26 and 28. The electrodeplates 40 can be a variety of shapes and sizes. In the embodiment, theelectrode plate is a thin plate of steel or copper, although othersuitable materials and shapes are also acceptable. The electrode platescan be made out of any of the conventional materials typically used forelectrodes. The material can be virtually any type of conductive metal.

[0038] As shown in FIG. 6 and 9, the electrode plate 40 includes thesame number of holes as dimples in the heat transfer plates. The holesare arranged in a grid-like pattern identical to the dimple arrangementof the first and second heat transfer plates. The insulator holes 44 inthe electrode plate are aligned with the insulator-engaging dimples 20and 26 of the first and second heat transfer plates. An insulatorstructure, to be described later, passes through and engages with acorresponding insulator hole 44. The electrode plate 40 is therebysupported and maintained in a constant position in the first fluidchannel 16. The electrode plate also holes 46 for allowing thestructural support dimples 22 and 28 to engage each other inside. Thestructural support holes 46 are sized to be slightly larger than thestructural support dimples so that the structural support dimples canpass through the hole without contacting the electrode plate. Thisclearance minimizes the risk of shock on the heat exchanger bymaintaining the heat exchanger to be electrically isolated from thevoltage of the electrode. Although the schematic in FIG. 9 illustratesthe structural support dimple being slightly spaced from each other, theend surfaces of the dimples are actually firmly pressed against eachother. The structural support dimples, in addition to the insulators,contributes to equal spacing between the heat transfer plates and helpsto minimize bending and expansion of the heat transfer plates. It shouldbe understood that in an application with low fluid pressure and smallamounts of fluid flow, the structural support dimples 22 and 28, and thecorresponding structural support holes 46 in the electrode plate may notbe necessary.

[0039] As shown in FIGS. 6 and 9, the electrode plates 40 include outerelectrode surfaces 42 on each side thereof. The refrigerant flowing inthe first fluid channels 16 flows along the outer electrode surfaces 42.The provision of an electrode plate 40 in the first fluid channels 16provides enhanced heat transfer between the refrigerant flowing in thefirst fluid channel and the heat transfer fluid flowing in the secondfluid channel, for reasons which will be described below. It ispreferable to place the electrode plate 40 in the first fluid channel 16equally spaced between the first and second heat transfer plates 12 and14 in order to provide equal electric fields on both sides of theelectrode plate. Preferably, the electrode plate is configured to beonly slightly spaced from the edge, or outer periphery, 56 and 58, ofthe first and second heat transfer plates, as best shown in FIGS. 5 and9. FIG. 5 shows the positioning of the electrode plate relative to aheat transfer plate. The holes in the electrode plate have been removedin FIG. 5 in order to simplify the drawing. The plate heat exchanger isdesigned to maximize the amount of heat transfer surface covered by theelectrode plate while also avoiding electrical contact with the heattransfer plates. In the embodiment shown, the electrode plate is roughlytrapezoidal.

[0040] The refrigerant channels 16 are sealed by end surfaces 60 and 62of the first and second heat transfer plates. The end surface 60 of thefirst heat transfer plate 12 is recessed from the flat surface 24 of thefirst heat transfer plate in a manner similar to structural supportdimples 22. The end surface 62 of the second heat transfer plate 14 isrecessed from the flat surface 30 of the heat transfer plate in a mannersimilar to structural support dimples 30. The first and second heattransfer plates are typically welded together at end surfaces 60 and 62along weld line 63. Other suitable attachment methods, such as pressfitting, are also acceptable.

[0041] When the plate heat exchanger is used as an evaporator, the outerelectrode surfaces 42 of each electrode plate 40 will be substantiallysmooth (except for holes 44 and 46). The smoothness of the outerelectrode surfaces 42 minimizes the electric field intensity along thesurfaces 52. The flat surfaces 24 and 30 of the first and second heattransfer plates along which the refrigerant flows in the refrigerantchannels 16 are provided with surface irregularities. The provision ofsurface irregularities on these refrigerant flow surfaces of the heattransfer plates 12 and 14 increases the surface area of the refrigerantflow surfaces in order to increase the heat transfer which occurs acrossthe heat transfer plates 12 and 14. The electrode plate 40 produces anelectric field on the refrigerant flow surfaces of the heat transferplates when a voltage is applied to the electrode plate. The electricfield is intensified at the surface irregularities, causing the liquidrefrigerant to be pressed against the inner surface irregularities ofthe refrigerant flow surfaces of the heat transfer plates, therebyincreasing the heat transfer rate significantly.

[0042] The inner surface irregularities on the refrigerant flow surfacesof the heat transfer plates 12 and 14 can be of a wide variety of sizesand shapes. The inner surface irregularities can be virtually any typeof surface irregularity including, but not limited to, cross-groovemicrofins, porous coatings, scratched surfaces, sintered surfaces,abraided surfaces (such as sand blasted surfaces), and dimpled surfaces.The surface merely needs to have numerous acute peaks and valleys sothat the electric field is intensified along the refrigerant flowsurfaces. Almost any type of surface irregularity will be useful withthe present invention.

[0043] It is desirable to maximize the roughness of the refrigerant flowsurfaces of the heat transfer plates for evaporation. As the surfacebecomes more rough, the electric field becomes more intense. Theelectric field becomes particularly intense at the sharp points of thesurface roughness. An additional benefit of increasing the roughness ofthe surface is that less voltage is required. Theoretically, the idealshape for the irregularities would be infinitely thin needles thatextend radially from the refrigerant flow surfaces to just short of theouter surface 42 of the adjacent electrode plate 40. This shape willdraw the maximum electric field around the irregular surface, therebymaximizing the heat transfer rate. Much less power is needed in order toobtain the desired heat transfer characteristics with such a shape.However, it may not be feasible to have such a design because ofpractical constraints such as electrode plate manufacturing limitations.It is believed that the optimum design will be a compromise, achieved bybalancing the various factors such as electric field, pressure drop,fluid flow, and shape and size of the surface irregularities, to achievea optimum design for a given heat exchanger.

[0044] While it is desirable to maximize the roughness of the innersurfaces of the heat transfer plates defining the refrigerant channel,it is also desirable to minimize the size of the gap between theelectrode plate and the refrigerant flow surfaces of the heat transferplates. The optimum size of the gap takes into consideration both thesize of the surface irregularities and the resulting pressure drop fromthe gap. It is desirable to have the gap be only slightly larger thanthe surface roughness. However, if the gap is too small, the pressuredrop will become too large. Therefore, it is important to balance theseconsiderations for each specific application.

[0045] In accordance with the present invention, and as previouslydiscussed, insulators are provided for electrically insulating eachelectrode plate from the adjacent heat transfer plates and forsupporting the electrode plate in its respective refrigerant channel. Asembodied herein and shown in FIGS. 7 and 9, a plurality of electrodeinsulators 64 prevent the electrode plate 40 from making electricalcontact with the heat transfer plates 12 and 14. The insulators can beof any variety of sizes and shapes. In the embodiment shown in FIGS. 6and 9, insulators 64 include a first cylindrical portion 66, flexiblecantilever projections 68, ramped protrusion 70, and an outer hollowcylindrical member 72. The first cylindrical portion 66 is sized toclosely fit inside the insulator dimple 20 of the first heat transferplate so that the insulator 64 is held firmly within dimple 20. Theprojections 68 extend axially from the first cylindrical portion 66, andare flexible. The projections are sized to fit inside the insulatorholes 44 of the electrode plate. The ramped protrusions 70 form a snapfit connection with the outer hollow cylindrical member 72. The outercylindrical member 72 is sized to closely fit inside the insulatordimple 26 of the second heat transfer plate so that the insulator isfirmly held within dimple 26.

[0046] Insulators 64 support the electrode plate so that the electrodeplate 40 is positioned midway between the refrigerant flow surfaces ofthe refrigerant channel 16. Insulators 64 also prevent the electrodeplate 40 from contacting any portion of the heat transfer plates. Thenumber of insulators matches the number of insulator holes in theelectrode, as well as the number of insulator dimples for each pair offirst and second heat transfer plates. A smaller or greater number ofinsulators can be used. Insulators can be made out of any type ofsuitable insulating material, typically plastic or ceramic. Theinsulators can be of a variety of sizes and shapes. The insulators shownin FIGS. 7 and 9 are exemplary only.

[0047] The pairs of heat transfer plates can be assembled by a varietyof methods. In a typical method of the present invention, the insulators64 are placed in each of the insulator holes 44 of the electrode plate.While inserting the ramped protrusions 70 into the insulator holes 44 ofthe electrode plate, the ramped protrusions are squeezed together sothey fit inside the holes 44. The electrode plate 40 is then slid alongthe length of the projections 68. The outer hollow cylindrical member 72is then slid over the ramped projections and snapped into position oncethe ramped projections extend completely through the cylindrical member72. The insulators 64 can now be slid into the insulator dimples 20 ofthe first heat transfer plate 12. Next, the second heat transfer plate14 is positioned over the hollow cylindrical member 72 and theinsulators are slid into each of the aligned insulator dimples 26 of thesecond heat transfer plate 14. The first and second heat transfer platesare now squeezed together so that the structural support dimples 22 and28 are firmly pressed against each other, and so that the insulators aretightly positioned inside their corresponding insulator dimples. The endsurfaces 60 and 62 can now be attached together by any known method,such as welding, in order to form the refrigerant channels 16.

[0048] These pairs of first and second heat transfer plates, can bestacked on top of one another to form the heat exchanger. A sealingmember, such as gasket 80 shown in FIG. 9, may be positioned between thepairs of first and second heat transfer plates, in order to define theouter periphery of the heat transfer fluid channels 18. In oneembodiment, the pairs of first and second heat transfer plates can bestacked on top of one another, with gaskets therebetween, and squeezedbetween two end plates 82 and 84 by bolts 86. Other known plate heatexchanger methods may also be utilized. It is useful to have anattachment method in which the plates can easily be removed from oneanother during maintenance. The attachment method should provide aneffective seal to prevent the loss of refrigerant and heat transferfluid.

[0049] In accordance with the present invention, the heat transferplates define apertures for entry and exit of the refrigerant and heattransfer fluid. Each heat transfer plate 12 and 14 defines a refrigerantsupply aperture 88, a refrigerant exit aperture 90, a heat transfersupply aperture 92, and a heat transfer exit aperture 94. Acorresponding tube can be provided for each respective aperture. FIG. 1shows the refrigerant supply tube 96 and refrigerant exit tube 98according to an embodiment of the present invention. Refrigerant supplytube 96 extends perpendicular to the heat transfer plates 12 and 14 andfits inside the refrigerant supply aperture 88. Refrigerant exit tube 98extends perpendicular to the heat transfer plates 12 and 14 and fitsinside the refrigerant exit aperture 90.

[0050] Holes or similar apertures are provided in each lengthwiseportion of the refrigerant supply tube 96 that is contained in the firstfluid channels 16 so that the refrigerant can exit the refrigerantsupply tube 96 into the first fluid channel 16. The holes or aperturescan be any suitable hole, aperture or other type of opening known in theart. Corresponding holes or apertures are also provided in thelengthwise portions of the refrigerant exit tube 98 that are containedin the first fluid channels 16 so that the refrigerant can exit thefirst fluid channel 16 and enter the refrigerant exit tube 98 to becarried away from the plate heat exchanger 10. Any suitable method ofallowing the refrigerant to enter the first fluid channel through asupply means and exit through an exit means is acceptable. In addition,the means for supplying and exiting the heat exchanger is not limited totubular members. Other known designs of transporting the refrigerant andheat transfer fluid are also within the scope of the present invention.

[0051] As embodied herein and shown in FIGS. 1, 2, and 5, a heattransfer fluid supply aperture 92 and corresponding heat transfer fluidexit aperture 94 are provided. A heat transfer fluid supply tube andheat transfer exit tube, not shown, are provided for the heat transfersupply aperture 92 and heat transfer fluid exit aperture 94,respectively, in a manner similar to the refrigerant tubes. Holes orsimilar apertures are provided in each lengthwise portion of the heattransfer fluid supply tube that is contained in the second fluid channel18 so that the heat transfer fluid may exit the heat transfer fluidsupply tube and enter the second fluid channel 18. Openings and designssimilar to those contemplated for the refrigerant tubes may be utilized.The heat transfer fluid, typically water, will enter the second fluidchannels 18 through the openings in the heat transfer supply tube of theheat transfer supply aperture 92, flow downward along the heat transferfluid flow surfaces of the heat transfer channel and exit the secondfluid channels 18 through similar openings in the heat transfer exittube of the heat transfer fluid exit aperture 94. The heat transferfluid then exits the plate heat exchanger 10 in a cooled state throughthe heat transfer fluid exit aperture 92 and heat transfer exit tube.

[0052] The preferred heat exchanger, as described in the presentinvention, is a counterflow-type of plate heat exchanger where the heattransfer fluid and refrigerant flow in opposite directions through theflow channels.

[0053] In the embodiment shown in FIGS. 1-10, heat transfer fluidaperture 92 is provided on the upper portion of the heat exchanger 10,whereas heat transfer fluid exit tube 94 is provided on the lowerportion of the plate heat exchanger. The refrigerant supply aperture 88is provided on the lower portion of the plate heat exchanger 10, whereasthe refrigerant exit aperture 90 is provided on the upper portion of theplate heat exchanger 10. It should be understood that the plate heatexchanger could be modified so that the refrigerant enters the heatexchanger at the top and the heat transfer fluid enters at the bottom.In addition, the supply and exit tubes may be of any variety of sizesand shapes that are known in the art, and are not limited to theparticular configuration shown in the drawings.

[0054] It should be understood that the plate heat exchanger shown inthe drawings is exemplary only. A variety of conventional plate heatexchangers are suitable for use with the present invention.

[0055] In accordance with the present invention, the heat exchanger alsoincludes an electrical connection structure for imparting voltage on theelectrode plates. As embodied herein and shown in FIGS. 1, 5, and 6, anelectrical connection structure 100 is provided for connecting theelectrode plates 40 to a voltage source (not shown). In the preferredembodiment, the electrical connection structure is in the shape of a rodthat extends longitudinally in the refrigerant exit tube 98. The rodpreferably includes threads so that the rod may be threaded through theelectrode plates. In the embodiment shown in FIGS. 5-6, each electrodeplate 40 is provided with a tab 102 having an hole 104 for the rod. Thehole 104 of the tab 102 preferably includes internal threads for matingwith external threads of the rod 100. The provision of threads providesfor an improved connection between the rod and the hole. The threadedrod can simply be threaded through each of the aligned holes 104 of theelectrode plates 40. The rods may be connected to the electrode platesby a variety of other connection methods besides the threaded rod andhole described above. Any alternate suitable connection method isacceptable. For example, the rod may be connected to the electrode platewith a compression fit inside the hole 104 of tab 102. In order toconnect the rod to the electrode plate, the rod can be first frozen andthen inserted into the hole 104. As the temperature of the rod graduallyincreases, the diameter of the rod will increase so that it is tightlyfit inside the hole 104 of tab 102. In another alternate method, a wireis passed through or wrapped around each of the electrode plate tabs.

[0056] All of the above methods allow for a relatively simple assemblyand disassembly of the electrical connection structure to and from theelectrode plates. A variety of other suitable attachment methods canalso be envisaged, as long as they provide for good mechanical andelectrical connections.

[0057] The voltage is provided to the electrode plate from a voltagesource applied to input connection 106. In the embodiment shown in FIG.1, the input connection 106 passes through the wall of the refrigerantexit tube 98. The input connection 106 shown in FIG. 1 is a ceramicinsulator in the shape of a spark plug, but with no gap for a spark. Theinput connection can be located at a variety of locations, for example,FIG. 10 shows an embodiment wherein a input connection 108 is located atthe end of the refrigerant exit tube 98.

[0058] The electrode plates are maintained at high voltages relative tothe heat transfer plate, preferably between 5 and 30 kV. Therefore, ahigh voltage power source is required. For example, in an embodiment tobe described below with a 100 ton capacity, a voltage of approximately20 kV is desirable. The suitable voltage range varies depending upon thesize, water flow, cooling rate desired, and selected materials of theplate heat exchanger. A wide variety of direct current high voltagepower sources are suitable for connection with the input connection 106(or 108) of the present invention. For example, a power source similarto that used in a television, or for lab instrumentation can be adaptedfor use with the present invention. It is desirable to minimize theamount of money expended on supplying power to the electrode plates.Therefore, it is desirable to have a system where a minimal amount ofvoltage will result in greatly enhanced heat transfer.

[0059] For any given application, the increase of the voltage throughthe electrode plates significantly increases the heat transfer rate ofthe heat exchanger, up until a point where the increased heat transferbecomes minimum or is so small as to not equal the cost for increasedvoltage. The best voltage for a given application can be determinedthrough empirical testing. Generally, the voltage can be increased to apoint where it is practically unfeasible to measure any increase in heattransfer. At this point the heat transfer rate is nearly infinite. Oneaspect of the present invention is to apply a sufficient voltage toachieve close to maximum potential heat transfer, while minimizingenergy costs.

[0060] The provision of an electrode plate in the refrigerant channelprovides enhanced heat rate between a refrigerant flowing around theelectrode plate and a heat transfer fluid flowing on the other side ofthe heat transfer plates. As embodied in an evaporator made inaccordance with the invention, the refrigerant flow surfaces of eachpair of heat transfer plates are provided with surface irregularities.The provision of surface irregularities on the refrigerant flow surfacesof the heat transfer plates increases the surface area of therefrigerant flow surfaces, and increases the heat transfer which occursacross the heat transfer plates. An electrode plate is provided toproduce an electric field on the refrigerant flow surface of each heattransfer plate when a voltage is applied to the electrode. The electricfield is intensified at the surface irregularities, causing therefrigerant to be pressed against the surface irregularities on therefrigerant flow surface of the plates, thereby enhancing the heattransfer rate across the plate significantly.

[0061] The plate heat exchangers according to the present invention havean improved heat transfer coefficient. Because of the large increase inheat transfer coefficient that occurs with the present invention, thesize of the heat exchangers for a particular application can besignificantly decreased. Therefore, the present invention is especiallysuitable for HVAC systems where size constraints are important.

[0062] The operation of the apparatus will be described below. In thepreferred embodiment, the heat exchanger is an evaporator, however, thepresent invention can also be used in a condenser with minormodifications which will be described later. For the sake of thediscussion below, the operation will be described with regard to anevaporator.

[0063] A first fluid comprising a refrigerant flows into a refrigerantsupply tube 96 that passes into the refrigerant supply aperture 88. Therefrigerant then flows into each of the first fluid channels 16 throughholes or apertures in the lengthwise portions of the refrigerant supplytube 96 that are located in the first fluid channels. The refrigerantflows upward from the bottom of the plate heat exchanger to the top ofthe heat exchanger in the first fluid channels 16. As the refrigerantflows upward, it passes along the refrigerant flow surfaces of the heattransfer plates 12 and 14. A predetermined voltage is applied to each ofthe electrode plates 40, thereby creating an electric field on therefrigerant flow surfaces of each heat transfer plate. The electricfield forces the liquid refrigerant to be pressed up against surfaceirregularities provided on the refrigerant flow surfaces, therebyincreasing the heat rate to a second fluid. The refrigerant then exitsthe first fluid channel through holes or apertures in the refrigerantexit tube 88, and leaves the heat exchanger.

[0064] The refrigerant exchanges heat with a second fluid comprising aheat transfer fluid flowing on the opposite side of the heat transferplates, and preferably in the opposite direction. The heat transferfluid is typically water, with additives such as propylene glycol (PG)or ethylene glycol (EG) in order to prevent the water from freezing. Theheat transfer fluid flows into a heat transfer fluid supply tube thatpasses into the heat transfer supply aperture 92. The heat transferfluid then flows into each of the second fluid channels 18 through holesor apertures in the lengthwise portions of the heat transfer fluidsupply tube that are located in the second fluid channels. The heattransfer fluid then flows downward from the top of the plate heatexchanger to the bottom of the plate heat exchanger. As the refrigerantflows downward through the second fluid channel 18, it passes along theheat transfer fluid flow surfaces of the heat transfer plates 12 and 14,and transfers heat to the refrigerant flowing in the first fluidchannels 16. As the heat transfer fluid flows across the heat transferplates, the temperature of the heat transfer fluid decreases due to heattransfer to the refrigerant through the heat transfer plates. Therefrigerant is at a lower temperature than the heat transfer fluid,therefore, heat is transferred from the heat transfer fluid to therefrigerant, thereby cooling the heat transfer fluid, while heating andultimately evaporating some or all of the refrigerant.

[0065] The heat transfer fluid leaves the second fluid channels in acooled state through holes or openings in the heat transfer fluid exittube. The cooled heat transfer fluid, such as water, may then be used tocool ambient air via an HVAC system.

[0066] The present invention is suitable for use with plate heatexchangers having a wide range of sizes and shapes. The followingdescription is for one typical plate heat exchanger, and is not meant tobe limiting in any manner. The following are approximate sizes for onetypical plate heat exchanger, as well as sizes for variants of thetypical plate heat exchanger indicated in parenthesis: capacity=100 tons(0.001 to 1,000 tons); water flow rate=240 gallons/minute (0.001 to2,400 gallons/minute); refrigerant flow rate=1.6 kg/s (0.001 to 160kg/s); voltage=20 kV (5 to 30 kV); electrode plate thickness={fraction(1/32)} in ({fraction (1/64)} to {fraction (1/16)} in); heat transferfluid channel width={fraction (3/16)} in ({fraction (1/16)} to ½ in);refrigerant channel width={fraction (3/16)} in ({fraction (1/16)} to ½in); heat transfer plate thickness={fraction (1/32)} in ({fraction(1/64)} to {fraction (1/16)} in); width of heat transfer plate=15 in(0.5 to 120 in); height of plate=34 in (1 to 120 in); number ofrefrigerant channels=20 (1 to 1,000).

[0067] As is evident from the above description, the present inventionincludes a method for effectuating an exchange of heat between a heattransfer fluid and a refrigerant in a plate heat exchanger. The stepsinclude: providing a plurality of parallel heat transfer plates;providing an electrode plate inside each of a plurality of first fluidchannels defined by first surfaces of adjacent heat transfer plates,flowing the refrigerant through the plurality of first fluid channels,flowing the heat transfer fluid along a second surface of each of theheat transfer plates, the second surfaces of adjacent heat transferplates defining a second fluid channel for the heat transfer fluid; andapplying a voltage to each of the electrode plates to create an electricfield, the electric field increasing the heat transfer rate between therefrigerant and the heat transfer fluid. The step of applying a voltageto each of the electrode plates includes attaching an electricalconnector to each of the electrode plates to supply the voltage to theplurality of electrode plates. In one embodiment, the step of providinga plurality of heat transfer plates includes forming surfaceirregularities on the first surfaces of the heat transfer plates. Inanother embodiment, the step of providing electrode plates. In a furtherstep, the electrode plate may be electrically insulated from theadjacent heat transfer plates. The step of applying a voltage to theelectrodes typically includes applying a voltage between 5 to 30 kV.

[0068] Although the above description is directed toward the use of thepresent invention in an evaporator, the principles of the invention arealso suitable for a condenser. In a condenser, the surfaceirregularities will be provided on the outer surfaces 42 of theelectrode plates 40 and the smooth surface will be provided on therefrigerant flow surfaces of the heat transfer plates 12 and 14. Therough outer surfaces 42 of the electrode plate will promote a higherelectric field along the outer surfaces of the electrode plates. Theliquid refrigerant will be pulled toward the high electric field on theelectrode plate. Because the liquid refrigerant is being pulled awayfrom the refrigerant flow surface of the heat transfer surface, therefrigerant vapor will travel along the surface of the heat transferplates 12 and 14. In a condenser, the heat transfer fluid flowing in thesecond fluid channels will absorb heat from the higher temperaturerefrigerant flowing through the first fluid channels, thereby causingthe refrigerant to cool and condense in the tubes. The heat transferfluid, typically water, will then recirculate to a cooling system suchas a cooling tower.

[0069] The outer surfaces 42 of electrode plates 40 in the condenser mayhave a variety of different surface irregularities, similar to thosedescribed for the evaporator configuration. Suitable surfaceirregularities include, but are not limited to, cross-groove microfins,porous coatings, sintered surfaces, abrasions, and dimpled surfaces.Surface irregularities may also be provided by forming the electrodeplate as a wire mesh in one embodiment of the condenser.

[0070] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the apparatus and method forincreasing the heat transfer rate of a heat exchanger, use of theapparatus of the present invention, and in construction of thisapparatus, without departing from the scope or spirit of the invention.

[0071] Other embodiments of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. The present invention is suitable inany application where it is desirable to improve the heat transfercharacteristics between two fluids. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims.

What is claimed is:
 1. A plate heat exchanger for accommodating twocirculating heat exchange mediums, comprising: a plurality of heattransfer plates mounted in parallel relationship to each other definingalternating fluid channels comprising first and second fluid channels,the first fluid channel for containing a first heat exchange medium, thesecond fluid channel for containing a second heat exchange medium; andan electrode plate located in each first fluid channel and positionedgenerally parallel to and spaced from the heat transfer plates, theelectrode plate including outer electrode surfaces on each side thereofto produce an electric field, wherein either the outer electrodesurfaces of each electrode plate, or the surfaces of the heat transferplates surrounding each electrode plate and defining the first fluidchannel, include surface irregularities, and wherein the effect of theelectric field on the surface irregularities is an increase in the heattransfer rate between the first heat exchange medium and the second heatexchange medium.
 2. The plate heat exchanger of claim 1, furthercomprising insulators for electrically insulating the electrode platefrom the surrounding heat transfer plates, said insulators supportingthe electrode plate in its respective first fluid channel.
 3. The plateheat exchanger of claim 2, wherein said insulators contact the heattransfer plates that surround the electrode plate.
 4. The plate heatexchanger of claim 3, wherein said dimples are formed on the surfaces ofthe heat transfer plates and said insulators are fit with said dimples.5. The plate heat exchanger of claim 2, wherein said electrode plateincludes a plurality of holes for the insulators to pass through.
 6. Theplate heat exchanger of claim 5, wherein dimples are formed on thesurfaces of the heat transfer plates and said electrode plate includes aplurality of holes for accepting said dimples.
 7. The plate heatexchanger of claim 6, wherein said dimples for contacting the insulatorsand said dimples accepted by the electrode holes are stamped onto theheat transfer plates.
 8. The plate heat exchanger of claim 1, whereineach electrode plate is positioned substantially equidistant from thetwo adjacent heat transfer plates that define the first fluid channel.9. The plate heat exchanger of claim 1, wherein each heat transfer platedefines apertures for entry and exit of each of the first and secondheat exchange mediums.
 10. The plate heat exchanger of claim 9, furthercomprising an electrical connector for imparting electrical voltage onthe electrode plates, the electrode plates being electrically connectedto one another by the electrical connector.
 11. The plate heat exchangerof claim 10, wherein the electrical connector comprises one of a rod,wire, and threaded rod passing through one of the apertures for entryand exit of the refrigerant.
 12. The plate heat exchanger of claim 11,wherein each electrode plate includes a projection through which theelectrical connector may pass to provide said electrical connectionbetween the electrode plates.
 13. The plate heat exchanger of claim 12,wherein the electrical connector is compression fit inside an opening inthe electrode plate projection.
 14. The plate heat exchanger of claim 1,wherein the heat transfer plate surfaces surrounding each electrodeplate and defining the first fluid channels include surfaceirregularities, and the plate heat exchanger comprises an evaporator.15. The plate heat exchanger of claim 14, wherein the outer electrodesurfaces are substantially smooth.
 16. The plate heat exchanger of claim14, wherein the surface irregularities include one of cross-groovemicrofins, porous coatings, scratched surfaces, sintered surfaces,abraided surfaces, and dimpled surfaces.
 17. The plate heat exchanger ofclaim 1, wherein the outer electrode surfaces of each electrode plateinclude surface irregularities, and the plate heat exchanger comprises acondenser.
 18. The plate heat exchanger of claim 17, wherein the heattransfer plate surfaces surrounding each electrode plate and definingthe first fluid channels are substantially smooth.
 19. The plate heatexchanger of claim 17, wherein the electrode plate is a wire mesh. 20.The plate heat exchanger of claim 1, wherein said first heat exchangemedium in the first fluid channel comprises a refrigerant, and saidsecond heat exchange medium in the second fluid channel comprises a heattransfer fluid.
 21. A plate heat exchanger for accommodating acirculating refrigerant and heat transfer fluid, comprising: a pluralityof heat transfer plates mounted in parallel relationship to each otherdefining alternating flow spaces for a refrigerant and a heat transferfluid; and an electrode plate located in each refrigerant flow space andspaced from the adjacent heat transfer plates, the electrode plateincluding outer electrode surfaces on each side thereof to produce anelectric field, wherein the effect of the electric field is an increasein the heat transfer rate between the refrigerant and heat transferfluid.
 22. The plate heat exchanger of claim 21, wherein either thesurfaces of the heat transfer plates defining the refrigerant flow spaceor the outer electrode surfaces of the electrode plates include surfaceirregularities.
 23. The plate heat exchanger of claim 22 wherein thesurface irregularities include one of cross-groove microfins, porouscoatings, scratched surfaces, sintered surfaces, abraided surfaces, anddimpled surfaces.
 24. The plate heat exchanger of claim 21, wherein theelectrode plate is substantially flat-shaped and is substantiallyparallel to the heat transfer plates.
 25. The plate heat exchanger ofclaim 21, wherein the electrode plate is positioned substantiallyequidistant from the adjacent heat transfer plates in the refrigerantflow space.
 26. The plate heat exchanger of claim 22, wherein thesurfaces of the heat transfer plates defining the refrigerant flow spaceinclude the surface irregularities, and the application of said electricfield presses the refrigerant against the surface irregularities. 27.The plate heat exchanger of claim 22, wherein the outer electrodesurfaces of the electrode plates include the surface irregularities, andthe application of said electric field pulls the refrigerant away fromthe surfaces of the heat transfer plates defining the refrigerant flowspace.
 28. A heat exchanger assembly for use in an HVAC system,comprising: a stacked array of heat transfer plates mounted in parallelrelationship to each other to define a plurality of first flow spacesfor a first heat exchange medium and a plurality of second flow spacesfor a second heat exchange medium; a plurality of electrode plates, anelectrode plate being positioned in each of the first flow spaces, theelectrode plates having electrode surfaces to produce an electric field,wherein the effect of the electric field is an increase in the heattransfer rate between the first heat exchange medium and the second heatexchange medium.
 29. The heat exchanger assembly of claim 28, whereineach heat transfer plate includes a first heat exchange medium flowsurface defining the first flow space, either the first surface of eachheat transfer plate or the outer surfaces of the electrode platesincluding surface irregularities.
 30. The heat exchanger assembly ofclaim 29, wherein the first heat exchange medium flow surface of eachheat transfer plate includes surface irregularities, and the plate heatexchanger comprises an evaporator.
 31. The heat exchanger assembly ofclaim 29, wherein the outer surfaces of each electrode plate includesurface irregularities, and the plate heat exchanger comprises acondenser.
 32. The heat exchanger assembly of claim 29, wherein theelectrode plate is positioned substantially equidistant from theadjacent heat transfer plates in the refrigerant flow space.
 33. Amethod of exchanging heat between a heat transfer fluid and arefrigerant in a plate heat exchanger, comprising the steps of:providing a plurality of parallel heat transfer plates; providing anelectrode plate inside each of a plurality of first flow spaces definedby first surfaces of adjacent heat transfer plates; flowing therefrigerant through the plurality of first flow spaces; flowing the heattransfer fluid along a second surface of each of the heat transferplates, said second surfaces of adjacent heat transfer plates defining asecond flow space for the heat transfer fluid; and applying a voltage tothe electrode plates to create an electric field, said electric fieldincreasing the heat transfer rate between the refrigerant and the heattransfer fluid.
 34. The method of claim 33, wherein said step ofapplying a voltage to the electrode plates includes attaching anelectrical connector to each of the electrode plates to supply thevoltage to the plurality of electrode plates.
 35. The method of claim33, wherein the step of providing electrode plates includes formingsurface irregularities on the first surfaces of the heat transferplates.
 36. The method of claim 33, wherein the step of providingelectrode plates includes forming surface irregularities on the outersurfaces of the electrode plates.
 37. The method of claim 33, furthercomprising the step of electrically insulating the electrode plate fromthe adjacent heat transfer plates.
 38. The method of claim 33, whereinthe electrode plate is positioned substantially equidistant from theadjacent heat transfer plates.
 39. The method of claim 33, wherein thestep of applying a voltage to the electrode plates includes applying avoltage between 5 to 30 kV.
 40. The method of claim 39, wherein theapplied voltage is approximately 20 kV.
 41. A plate heat exchanger foraccommodating a circulating refrigerant and heat transfer fluid,comprising: opposing plates with sets of aligned outwardly and inwardlyextending dimples, the first set of aligned dimples extending inwardlytowards each other, the second set of aligned dimples extendingoutwardly away from each other to create an open space; an electrodeplate positioned between the opposing plates, the electrode plate havingholes aligned with the dimples; and an insulator in the open space tohold and be positioned in the outwardly extending dimples and to passthrough an aligned hole of the electrode plate, wherein said inwardlyextending dimples pass through an aligned hole of the electrode plateand touch each other.